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Living Shorelines Types from large to small Downsizing a Living - - PowerPoint PPT Presentation
Living Shorelines Types from large to small Downsizing a Living - - PowerPoint PPT Presentation
Living Shorelines Types from large to small Downsizing a Living Shoreline; Retail-scale Options for Private Properties on Exposed, Rapidly-Eroding Coasts David d. McGehee, P.E., D.CE Emerald Ocean Engineering LLC and Taylor Chips
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Project Location
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Existing Conditions
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Owner's Mission
Reduce Upland/Shoreline Erosion Maintain Recreational Beach Be a Good Neighbor Utilize a Living Shoreline (“. . . like Project Greenshores”)
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Average Erosion @ Project 1997 - 2013 ~ 2 ft/yr
Over 1 ft/mo from 2008 - 2010
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Site Analysis
Calculated Net LST Potential (cu yd / yr)
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LST potential shows accumulation:
Why isn't the project accreting? No southern sediment supply If shorelines are retreating, where is all that eroded sand going? Offshore
(see offshore profiles)
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CONCEPTS
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Design Challenges/Design Strategies
Optimize reef bw performance to:
Eliminate/reduce upland erosion & offshore transport Sill; dissipate high steep waves; pass low long waves Maintain the saltmarsh Average Hs < Hth (Douglas & Stout, 2004) Permit adequate longshore transport Salient good; tombolo bad; bobcat OK Adapt to sea level rise Rise with it: 1) maintenance {cheap}; 2) oysters {free} Survive extreme events Stay low; stay flat
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Design profile
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DESIGN PLAN
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03/13/16
Voluntary Adaptive Management Plan
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CONSTRUCTION
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Cost Comparison
For 155 ft of shoreline protection: Traditional Bulkhead - $40-60 K Living Shoreline – $ 70 K Offshore Emergent Breakwater > $100 K
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State-mandated Monitoring
11 Profiles extending ~200'
- ffshore
250' N & S of project bounds Neighborhood seminars Semi-annually, 3 yrs
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1Week Post Construction
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I Week Post Construction
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1 Year Post Construction
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1 Year Post Construction
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Missions Accomplished ! (?)
OWNER'S DESIGNER'S
- Reduce erosion
√
- Recreational beach √
- Neighborly
√√
- Living Shoreline √√√
- Reduce erosion
A
- Maintain saltmarsh
A
- Allow LST
C ??
- Survive
Incomplete
- Adapt to SLR
– Cheap
A
– Free
D
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LESSONS
- Saltmarsh vegetation can thrive on
exposed bay shorelines
- Submerged Reef BW perform well in
X-shore dominated shorelines
- Submerged reef BW can be:
– Reef habitat as valuable as marsh – Breakwaters as effective as emergent bw
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??Questions??
Low tide visitor ↑ High tide visitor →
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Offshore Profiles => Offshore Trx. 15 yrs upland erosion ~ Vol. > P0
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Profile 4S – Local Effects (LST-o-meter)
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